1. Field of the Invention
The present invention relates to a control method of a robot and a control device for executing this control method, which are applicable to the deburring work for the machined parts or cast parts to be executed by a robot which operates in accordance with a taught program.
2. Description of the Related Art
The use of a robot for deburring work is a known prior art. Many attempts have been made for using a deburring robot to substantially save much manpower required for deburring work in the finishing stage of machined parts and cast parts.
When using a deburring robot, a path along the deburring line and a fixed moving speed are taught to the robot, and deburring is performed through the playback operation of the robot. In practice, however, in many instances, it is difficult to provide the best working conditions suitable for the state of burrs formed, or the properties of burrs, to be removed in the deburring work using a deburring robot.
One of the main reasons for this is that the burrs are formed in irregular shapes and conditions on actual workpieces (machined parts, cast parts, etc. are hereinafter simply called workpieces). This situation will be explained with reference to FIG. 1. FIG. 1 schematically shows part of burrs formed along the periphery of a workpiece. P.sub.1 and P.sub.2 are taught points. When a deburring robot is played back, the robot carrying a deburring tool removes burrs successively while moving along the straight line (or circular arc) section P.sub.1 P.sub.2. In many instances, the burrs formed on the deburring line are not uniform in size, strength, density, etc. As shown in FIG. 1, in many instances, the burrs occur not only irregularly but also in different types such as one represented by that of portion A, in which relatively small or weak burrs (hereinafter referred to simply as "small burrs") are formed, one represented by that of portion B, in which relatively small burrs and relatively large or hard burrs (hereinafter referred to simply as "large burrs"), one represented by that of portion C, in which relatively large burrs are relatively densely formed, and one represented by that of portion D, in which burrs are scarcely formed.
Essentially, it is considered to be reasonable to change the moving speed (deburring speed) or the pressing force of the deburring robot depending on the type of burr, or to take other measures.
However, the irregularity of burr formation varies depending on individual workpieces. Also, it is extremely difficult to accurately predict the types of burrs (as those represented in A to D), portion of workpiece on which burrs are formed, and area of the workpiece in which burrs are formed. For this reason, it has been a common practice to estimate the maximum burr size, maximum burr density, etc. throughout the whole deburring section of workpiece to determine the moving speed of robot based on this estimate. For example, in the case of FIG. 1, the moving speed has been selected by assuming that the whole section is in the condition of taking considerable time in removing burrs as with the case of section C. Therefore, the moving speed of the robot at the sections such as section A where burrs can be removed easily as compared with section C becomes slower than needed, which is a major factor of decreasing work efficiency.
If the robot moving speed is increased to enhance the working efficiency, burrs are removed incompletely at section C, so that finishing quality is degraded. That is to say, it is very difficult to simultaneously meet both requirements of shortening of deburring time and increasing of working accuracy.
Further, at the portion where large burrs are present like section C, the tool is strongly pressed against the burrs, so that the tool is prone to be subjected to an excessive load. A method, which has actually been practiced for avoiding the excessive load, is to install a floating mechanism on the deburring tool supporting portion. When the floating mechanism is used, however, there will be a greater chance for the tool to pass the burrs without removing them by simply moving along their contours, especially when the burrs are large in size. Besides, it is hard to estimate the ratio of unremoved burrs, and thus it is not easy to assure required machining quality on the systematic bases.
If the characteristic of the floating mechanism, in which the irregularity of burr formation can be absorbed, is utilized, and the robot path is taught so that the tool presses the workpiece a little excessively, the number of revolutions of deburring tool cutting edge decreases when a large burr is encountered during the playback deburring work, and the restoration of number of revolutions just after the tool passes through the burr portion sometimes delays. This is considered to be caused by that the tool is always kept in contact with the workpiece, since the programmed playback path of the robot has been brought closer to the workpiece. If such a phenomenon occurs, there is a possibility that deburring work immediately after the tool has passed the large burr portion will not be done properly.
Further, with the prior art, as long as the properties of the burr varies depending on the individual workpieces, it is extremely difficult to estimate the ratio of complete deburring before actually checking the result of deburring for individual workpieces. Thus, has been employed is a method such that each workpiece which has undergone the deburring process is checked so that incompletely deburred workpieces can be picked out for re-deburring. Such a method, however, is not good enough for executing the all the processes of the deburrring work with high efficiency.
As described above, the conventional deburring robot technology has unsolved important problems: the moving speed of robot cannot be determined so as to rationally accommodate the irregularity of burr properties; it is difficult to assure stable working quality for the whole working path including the portion where large burrs are formed; and a suitable index for estimating the achievement of burr removal for each workpiece is not given.